We have observed more intense effect of smoking on perinatal mortality with decending social status (Rush and Kass, 1972). In a recently completed randomized controlled trial, nutritional supplements in pregnancy completely protected against the low birth weight associated with heavy maternal smoking in a deprived, public clinic population. The first objective of this research is to explore further, among these heavy smokers, the effects of the nutritional trial on other outcomes of pregnancy, including placental structure and function, and newborn and one year old growth and development, particularly psychological function. The second objective is to test whether the data of four large surveys of Pregnancy (The 1958 British Perinatal Mortality Survey, The 1970 British Births Study, The Cardiff Births Survey, and The Jerusalem Perinatal Study) support the possibility of nutritional mediation of the more intense effect of smoking with descending social status. Depressed maternal weight and/or weight gain in pregnancy have sometimes been associated with smoking, and sometimes not. The hypothesis that nutritional effects are linked with social status could explain these seemingly contradictory observations. The contribution of smoking to the social class gradient of perinatal outcomes will be quantified. Next, we will study the extent of potentation of the effect of smoking by low maternal weight and/or weight gain. We will then judge whether the effect of smoking on the fetus is in part mediated by lowered weight and/or weight gain, and whether this path in part accounts for the interaction of smoking and social class on perinatal outcome. These studies are meant not only to improve our understanding of smoking in pregnancy, but to elicit possible strategies for prevention.